Starting a new yagi today

[RickC.]

Got a break in the rain, had to move fast to try to make the most of it.

After trying a couple more things, it was clear the plywood mount for the reflector element just was not going to cut it. So, I did:

A 4 foot piece of angle aluminum ¾” x ¾” x 1/8” was used (I wanted 1” x 1” but the local Lowes didn’t have any in 4’ pieces—I think this will be fine though). I wasn’t sure whether I’d still need to use the cord so I left the standoff in place:

The reflector went back on with stainless hose clamps leftover from a quad a few years back and I was able to prime the shiny metal before the rain started again:

Noticeable improvement. I may do the same for the driven element:

It’s getting’ there, despite the setback and having to go with Plan B—that happens a lot when you’re using materials for something other than their intended use:

Still shooting for getting this up in the air on Monday but if The Weather Channel is accurate, it may be next weekend.

 

[Captain Kilowatt]

I can empathize with your frustrations. I have a shiny new Explorer-14 to put up but I have yet to find a combination of half decent warm temps, NO wind, and a day off that is not my first day after coming home in the morning from a night shift. :headbang I need to strip the tower of all the crap on it before I can install the new antenna. Hopefully your luck is better than mine.

 

[HomerBB]

Looking really good. I have my fingers crossed that the changes as well as the weather will be all right. I am anxious to see this thing in action.

 

[RickC.]

This is turning out to be a long project because of the rain delays, but I decided to change the plywood mount for the driven element also to angle aluminum. 1 x1 x 48”. Getting ready for Plan B:

Feedpoint now- the 20m driven element stays in a straight line on top of the pole, while the 10m element is tie-wrapped and glued to a point on the remaining plywood to give about 3” separation between the two and keep it away from the aluminum mount:

Full view of Plan B, showing the 3” pieces of plastic tubing at the end of the angle aluminum to keep the 10m element spacing out that far. This was all spray painted flat black later. You can see at the top the wires go back to the orginal arrangement, being spaced only by the diameter of the pole. This is exactly the opposite of what you’d usually want with a fan dipole, but this keeps the element light so there won’t be so much out there waving in the wind. No telling what effect this will have on interactance, and it’ll be interesting to see if the angle aluminum is resonant around 118 MHz as an open sleeve dipole:

The ends of both driven elements are left a bit long for tuning and will be secured once that’s done. This is one end of the 10m DE:

I have chores/errands to run tomorrow (figures), so I’m shooting for Sunday afternoon getting this up in the air to begin tuning. Somebody do a short-term drought dance for me!


Rick

 

[HomerBB]

Lots of changes and progress. No doubt this thing is growing. Hopefully, my drought dance will help, or was that the rain dance I did. . . .?

 

[RickC.]

OK, back on it today after a few days of plumbing and some other household emergencies.

Hairpin match and mast-to-boom bracket in place:

The match itself is 7x22 antenna wire, shorting bar just 14 ga solid copper soldered to two alligator clips to make adjustments easier. I can either replace that with a jumper and solder it once the tuning is done, or solder the clips to the hairpin, don't know yet which I'll do.

Had two silver plated PL-259s come apart today while preparing the RG-213 for this antenna. Gave up and called it a day. For today anyway.

It has never taken me this long to finish an antenna, between the weather and other stuff that has come up. I don't want the time this has taken to discourage anyone from building something, that's just the way it has worked out with this one so far.

More tomorrow, I hope!

Rick

 

[RickC.]

With all the delays it took forever to get to this point, but it’s finally in the air!

Only 20 feet up until I get the feedline connected, then I’ll tune it at around 24-25 feet. Other antennas have not shown a huge difference in tuning between that height and 33-35 feet, so I’ll hope for the best.

I’d already decided I didn’t want to deal with a big coil of RG-213 and didn’t want to lay out 50-75 bucks for a commercial balun. The Palomar Engineers balun kit ($17 plus shipping) caught my eye:

5 ferrite beads and heatshrink. I’ll post the instructions here if anyone is interested (you may be able to read them from the pic), but installation was no sweat.

I was at a stopping point since my tube of RTV in the garage lost its top sometime since the last time I used it, so I thought I’d put these up before I make another trip to Lowes. Hope to at least start on the tuning later today.

Rick

 

[HomerBB]

Looks good.

 

[RickC.]

Tuning so far--

It's too hot up there right now for both me and the 259-B, but so far the 20m tuning is coming along nicely. First test resonated at 13.695, I have it at 14.115 right now- 65 ohms, x=0. Changing the position of the shorting bar doesn't make much difference unless I move it 6" or so, then it just doesn't play nice. At this point I have taken exactly 5" off each side of the 20m driven element. Given the need for a capactive driven element and the velocity factor of the insulated wire (and possible dielectric of the fiberglass pole) this seems about right. So far, so good.

10m may be a challenge. It's not exactly resonant anywhere close to there right now but has VSWR of below 2:1 at 25.860. I'll get back on that this evening.

I have the shorting bar on the hairpin set at 15 1/2", so that will hopefully give me some leeway if I need to jockey it around for 10m this afternoon.

 

[mackmobile43]

Tuning so far--

It's too hot up there right now for both me and the 259-B, but so far the 20m tuning is coming along nicely. First test resonated at 13.695, I have it at 14.115 right now- 65 ohms, x=0. Changing the position of the shorting bar doesn't make much difference unless I move it 6" or so, then it just doesn't play nice. At this point I have taken exactly 5" off each side of the 20m driven element. Given the need for a capactive driven element and the velocity factor of the insulated wire (and possible dielectric of the fiberglass pole) this seems about right. So far, so good.

10m may be a challenge. It's not exactly resonant anywhere close to there right now but has VSWR of below 2:1 at 25.860. I'll get back on that this evening.

I have the shorting bar on the hairpin set at 15 1/2", so that will hopefully give me some leeway if I need to jockey it around for 10m this afternoon.

......................................................................................................

Would this excess amount of exposed center lead of your coax present any issues?

 

[RickC.]

Reasonable question.

That may look long, but it's not excess. The feedpoint terminals are 4" apart and the center conductor and shield have to be able to reach that from where the coax is flat against the boom without putting stress on either themselves or the feedpoint screws. If you look at the manual for any of the HyGain antennas that use a Beta match (their term for a hairpin match) they show both leads being 6" long. These are just a bit over 5" so that's not a big deal. Now the lead length could affect the length of the driven elements themselves, but that's not a problem. In the commercial beams they've got all that figured out: Have the coax leads X inches long, set the elements to X dimensions and this should be your VSWR curve. I don't have that to go by, but it really doesn't matter. That's the thing about building this stuff yourself, as long as you understand what you're about, just snip, tweak, and adjust until you have it tuned where you want it!

The big question I have is whether the spacing of the 20m yagi (8 feet, which was chosen to improve the f/b of the VE7CA design) will allow me to find a compromise feedpoint impedance on both bands I can live with. That may yet be possible, and 65 ohms is certainly liveable. Anytime I have built fan dipoles or other antennas using a common feedpoint for HF I've had the best results tuning the lowest band first, then adjusting the higher bands. That's the approach I'm taking here.

Unfortunately I'll have to wait until tomorrow to see how this plays out since the bottom fell out here (again) not long ago!

Thanks, we'll see how it works.

Rick

 

[RickC.]

WHEW! Tuning finished.

This was an adventure.

Long story short, I chased that 65-69 ohms all over the 20 meter band. That would have been OK, but it just didn't make sense to me that the feedpoint impedance of a 2 element yagi at 1/8 wave spacing (roughly) would be that high with the inductive match. Since I was building this thing, I didn't want to just live with a 1.3:1 at best and 2:1 before reaching the band edges.

So on a whim I disconnected the match and measured it with direct coax feed through the balun. The resonant frequency immediately moved up 400 KHz, but it was 51 Ohms, x=1. Ok, made sense on a 2 element yagi, but let's see what it did to 10.

On 10 meters using the hairpin I could get a decent VSWR and resistance but could not get below 25 ohms capacitive which bugged me--maybe this idea just wasn't going to work after all. However, with direct feed this dropped to 7 ohms XC before trimming. Hmmmm...

Bottom line:

I had to solder wire back onto the ends of the 20 meter driven element and trim back up to bring the fr back into range, and ended up trimming about 4 inches off the 10 meter element. But it ended up as--

20 meters--

fr- 14.194, R=54, X=3 2:1 VSWR bw: 13890 - 14559

10 meters--

fr- 28315, R=52, X=0 2:1 VSWR bw: 28025 - 28595

Note that's direct coax feed (through a choke balun) on a 3 element yagi, which is not supposed to happen. These measurements were made at the end of the 75' RG-213 feedline I'm going to use. For whatever reason though, probably a happy accident of the interaction and spacing between the 2 driven elements, but there it is.

I would not have predicted this, but I'll take it. I'm having to relocate the shack upstairs and don't have everything ready yet so it will still be a few days before I can fire it up and see how it performs.

It was freakin' hot on that roof. Also, as much as I have come to love my old Palomar noise bridge over the years, the MFJ-259B makes this kind of thing SO much easier. Thanks for hanging in here with me on this thread, sorry it’s taken so long to get to this point. A monoband yagi built using this kind of construction would be simpler and faster.


Rick

 

[RickC.]

OK- in the air now. Final weight 18 lbs, boom height 36 feet:

The shack still hasn't been moved upstairs, but I toted the old TS-520 upstairs and ran the rotor cable and coax in the back door and put the Kenwood in a dining room chair. I had emailed a friend who is driving between Houston and San Antonio today who has an HR-2510 in his car-- unfortunately 10m rewarded me by shutting down...

I have to head over to the inlaws for Father's Day barbeque, but will have it on the air tomorrow. The tuning didn't changed at all on 10m at the new height, but it's more broadbanded now on 20.

(I don't recommened doing this kind of thing on the roof when it's in the mid-90s but I was on a mission and I had no choice. My left knee will be seeing a lot of aloe vera tonight.)


Rick

 

[HomerBB]

Well it certainly looks good. And the broadbanded surprise is a good detail, too.

 

[Moleculo]

This is a great homebrew write-up Rick...thanks for taking the time to take all of the pictures and write up all the details. The antenna looks great on the roof! Have you had a chance to get a feel for the F/B ratio?